[Coco] ML Question: MMU Block Switching

[Robert Gault]

William Mikrut wrote:
> I do have a another ML question about memory block switching.
> When processing I will have a controlling program setup at $1200
>
>          orcc     #$50    Interrupts off
> lda $ffa1     Load current page
> anda   #63
> pshs a           Push for later
> lda #$36 Map in Hi-res Text
> sta $ffa1     Tell MMU to switch page
> andcc  #$ef      Interrupts on
>
> Now I can manipulate data in $2000-$3FFF and essentially display text on
> the hi-res text screen.
>
> When I am done and ending the program I cleanup with this:
>          orcc #$50
> puls a
> sta $ffa1
> andcc  #$ef
>
> Is there any reason that would cause a program fault while my lower memory
> program is operating and the MMU is set to map in page 36 to $2000-$3FFF?
>
> My lower memory program is no where near $2000 in ending size.
>

Normally you would want andcc #$af since you disabled both FIRQ and IRQ with 
orcc #$50  where $50=%01010000.

If you have already turned on the Hi-res text screen via Basic, the above would 
work. As an alternative, you could use the default MMU value for $FFA1 and point 
the Hi-res text screen to $72000 using the registers $FF9D-$FF9E.

Actually you will need to post all of your program for us to tell what problems 
might arise. :)

Robert